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E.164: Integrating OCS 2007 R2 with voice

Hugh Marlor, UC integration and interoperability expert

Hugh Marlor, unified communications integration and interoperability expert

Since the release of OCS 2007 R2 there has been much discussion as to where telephone number manipulation to E.164 format can occur or where it must occur, (e.g., OCS normalization rules or media gateway manipulation tables). This blog presents the current functionality for telephone number manipulation provided in OCS 2007 R2 to help those deploying OCS 2007 R2 with telephony integration to understand when and where to do telephone number manipulation.

Telephone number manipulation is one of the key actions or processes that must be implemented when deploying OCS 2007 R2 along with voice integration, (i.e., placing and receiving phone calls to/from the PSTN). Microsoft recommends — although the product does not specifically require — that the E.164 telephone number format be utilized when storing and using telephone numbers within Active Directory.  This provides for the enforcing of a uniform standard for managing telephone numbers stored in AD and/or Outlook contacts. Using the E.164 format also enhances the end-user experience — or user experience (UX) as MS refers to it — by allowing such features as incoming calls to MOC to display not just the incoming phone number, but the calling person’s name and other information.

Standardizing on E.164 and media gateways

The description below applies to a scenario in which a company has agreed to standardize on E.164 formatted numbers — MS best practice. This explains why you will need some sort of media gateway if you decide to implement E.164 in OCS/AD. Exception: You are able to do the required number manipulations on the IP PBX, (i.e., providing you convince the team to agree to that). This discussion is also important when considering connectivity to the PSTN via SIP trunks, (e.g., Cisco CallManager 7.x server or a SIP trunk provider).

For more information see Optimized call routing and PSTN backup excerpted from Identifying issues in a multi-site Cisco UC deployment.

Working with SIP providers (e.g., BT, Sprint, Global Crossing)

When a provider installs a SIP trunk it is necessary (as with a PBX connection such as a QSIG trunk) that a discussion is conducted to understand how a particular SIP trunk provider will expect to receive digits for dialing (e.g., 10 digits, 11 digits, local calling digits, etc.). It also needs to be understood how a SIP provider will send digits to OCS.

Just because you are using a SIP trunk there is no reason to think service providers will provide or accept numbers in E.164 format. Until such a time that SIP trunk providers all accept and expect E.164 numbers, there will be a need for media gateways to do number manipulation when deploying OCS 2007 R2 with enterprise voice.

Inbound and outbound telephone number manipulation and where it must take place:

Outbound number manipulation

  • OCS 2007 R2 allows outbound normalization of destination numbers (called number) via normalization rules that convert the number to E.164 so that an Active Directory Reverse Look Up, (ADRLU) for an AD user’s tel URI (phone number) is successful. If the ADRLU returns “true” then the call would go via MOC to MOC , and if false then route to the mediation server for routing to the PSTN. The problem is that when the number arrives at the mediation server as E.164 there is no way to convert the called number to a dialable format for the PBX, (e.g., 10 digits with no “+”). This means in R2 you must manipulate the called number using tables on the media gateway.

The calling number in R2 is also subject to these restrictions in that you cannot manipulate those numbers within OCS, but must do that on the media gateway.

Inbound number manipulation

  • OCS 2007 R2 allows the manipulation of the called number so that it can be converted to an E.164 format for causing a successful ADRLU, (this is done by applying a location profile to the mediation server itself).
  • OCS 2007 R2 does not however allow the manipulation of calling numbers so it is necessary to use manipulation tables on a media gateway to convert the numbers to E.164 so that the inbound ADRLU is successful.

Additional information on E.164 telephone number manipulation:

About the blogger:

Hugh Marlor, UC integration and interoperability expert for and senior unified communications consultant, BT’s Professional Services Group.

As a senior unified communications (UC) consultant within BT’s Professional Services Group, combined with over 20 years of experience in IT, Hugh’s specialized experience in messaging, collaboration, project management and implementation combined with his proven ability to design, implement, and manage complex software and networking environments makes him a thought leader in the UC integration and collaboration space.

Send Hugh your questions about UC implementation or integration and read recent responses:

When do you need SAN fields for the OCS Pool Certificate?
What is a key component to successful OCS 2007 integration with our corporate phone system?
Error 500: Testing media gateway configurations for OSC 2007 R2

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